PHP calls the camera for real-time video encoding: practice from input to output

PHP calls the camera for real-time video encoding: practice from input to output

Abstract:
This article will introduce how to use PHP to call the camera for real-time video encoding. We will achieve this by using PHP's FFI extension and calling the ffmpeg library.

Keywords:
PHP, camera, video encoding, FFI, ffmpeg

1. Introduction
   With the advancement of modern technology, more and more applications require Live video processing. As a language widely used in web development, PHP often hopes to use PHP to process video streams. This article will introduce how to use PHP to call the camera for real-time video encoding, realizing the entire process from input to output.

2. Preparation
   First, we need to install the ffmpeg library and the FFI extension of PHP. It can be installed through the following command:

   sudo apt-get install ffmpeg
   sudo pecl install ffi

3. Writing code
   The following is a sample code that demonstrates how to use PHP to call the camera for real-time video encoding.

<?php
// 初始化
$ffi = FFI::cdef("
    typedef void * AVFormatContext;
    typedef void * AVCodecContext;
    typedef void * AVFrame;
    typedef void * AVPacket;
    typedef struct {
        int width;
        int height;
        int size;
        int format;
    } AVFrameInfo;
    
    AVFormatContext *avformat_alloc_context();
    int avformat_open_input(AVFormatContext **ps, const char *url, void *fmt, void *options);
    int avformat_find_stream_info(AVFormatContext *ic, void *options);
    void avformat_close_input(AVFormatContext **s);
    
    AVCodecContext *avcodec_alloc_context3(void *codec);
    void avcodec_close(AVCodecContext *avctx);
    void avcodec_free_context(AVCodecContext **avctx);
    
    AVFrame *av_frame_alloc();
    void av_frame_free(AVFrame **frame);
    
    AVPacket *av_packet_alloc();
    void av_packet_free(AVPacket **pkt);
    
    int av_read_frame(AVFormatContext *s, AVPacket *pkt);
    int avcodec_send_packet(AVCodecContext *avctx, AVPacket *avpkt);
    int avcodec_receive_frame(AVCodecContext *avctx, AVFrame *frame);
    
    int av_image_get_buffer_size(int pix_fmt, int width, int height, int align);
    int av_image_alloc(uint8_t *pointers[4], int linesizes[4], int w, int h, int pix_fmt, int align);
    void av_freep(void *ptr);
    void av_image_fill_arrays(uint8_t *dst_data[4], int dst_linesize[4], const uint8_t *src,
                              int pix_fmt, int width, int height, int align);
    void av_image_copy(uint8_t *dst_data[4], int dst_linesize[4],
                       const uint8_t *src_data[4], const int src_linesize[4],
                       int pix_fmt, int width, int height);
    void av_image_copy_plane(uint8_t *dst, int dst_linesize, const uint8_t *src, int src_linesize, int bytewidth, int height);
    
    void av_init_packet(AVPacket *pkt);
", "libavformat.so.58");

// 打开摄像头
$formatContext = $ffi->avformat_alloc_context();
$source = "/dev/video0";
$ffi->avformat_open_input(FFI::addr($formatContext), $source, null, null);
$ffi->avformat_find_stream_info($formatContext, null);

// 查找视频流
$videoStreamIndex = -1;
for ($i = 0; $i < $formatContext->nb_streams; $i++) {
    if ($formatContext->streams[$i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
        $videoStreamIndex = $i;
        break;
    }
}

if ($videoStreamIndex == -1) {
    die("未找到视频流");
}

// 获取视频流信息
$videoCodecPar = $formatContext->streams[$videoStreamIndex]->codecpar;
$videoCodec = $ffi->avcodec_find_decoder($videoCodecPar->codec_id);
$codecContext = $ffi->avcodec_alloc_context3($videoCodec);
$videoFrame = $ffi->av_frame_alloc();
$packet = $ffi->av_packet_alloc();
$frameInfo = FFI::new("AVFrameInfo");

// 设置解码器上下文参数
$ffi->avcodec_parameters_to_context($codecContext, $videoCodecPar);
$ffi->avcodec_open2($codecContext, $videoCodec, null);

while ($ffi->av_read_frame($formatContext, $packet) >= 0) {
    // 解码视频帧
    if ($packet->stream_index == $videoStreamIndex) {
        $ffi->avcodec_send_packet($codecContext, $packet);
        while ($ffi->avcodec_receive_frame($codecContext, $videoFrame) >= 0) {
            // 获取视频帧信息
            $frameInfo->width = $videoFrame->width;
            $frameInfo->height = $videoFrame->height;
            $frameInfo->size = $ffi->av_image_get_buffer_size($videoFrame->format, $videoFrame->width, $videoFrame->height, 1);
            $frameInfo->format = $videoFrame->format;
            
            // 分配输出缓冲区
            $outBuffers = FFI::new("uint8_t[4]");
            $outLinesizes = FFI::new("int[4]");
            
            $ffi->av_image_alloc(FFI::addr($outBuffers), FFI::addr($outLinesizes), $frameInfo->width, $frameInfo->height, $frameInfo->format, 1);
            
            // 复制解码后的图像数据到输出缓冲区
            $ffi->av_image_copy($outBuffers, $outLinesizes, $videoFrame->data, $videoFrame->linesize, $frameInfo->format, $frameInfo->width, $frameInfo->height);
            
            // 输出图像数据，可以自行处理例如将图像数据发送给Web页面的Canvas元素
            // 这里只是简单地输出一帧的数据
            echo $outBuffers[0];
            
            // 释放输出缓冲区
            $ffi->av_freep($outBuffers);
        }
    }
    
    $ffi->av_packet_unref($packet);
}

// 释放资源
$ffi->av_frame_free(FFI::addr($videoFrame));
$ffi->avcodec_close($codecContext);
$ffi->avcodec_free_context($codecContext);
$ffi->avformat_close_input(FFI::addr($formatContext));

?>

4. Conclusion
   This article introduces how to use PHP to call the camera for real-time video encoding. By using PHP's FFI extension and the ffmpeg library, we can easily output the camera's video stream to other devices or web pages. I hope this article can be helpful to developers who use PHP for video processing.

References:

• https://github.com/PHPFFI/PHPFFI
• https://www.ffmpeg.org/documentation. html

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